Method and device for page by page conveyance of a pre-printed striplike recording medium in a printer

ABSTRACT

A method and device to control a paper drive mechanism of an electrographic printer or copier by friction feed. Optical markings are provided on the recording medium, and a sensor scans an area of the recording medium for the optical marking during transport of the recording medium. An evaluation device evaluates the signals from the sensor for two successive markings corresponding to page length. High speed conveyance of the recording medium is controlled according to page length identified by the evaluation device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a method and to an apparatus forthe transport of pre-printed, web-shaped recording media, particularlycontinuous form paper in an electrographic printer. Paper, foilmaterial, labels or other materials can thereby be employed as theweb-shaped recording medium.

2. Description of the Related Art

The greatest variety of paper grades are employed when printing paper.What is referred to as margin-perforated paper is mainly employed in theelectrographic high-performance printer field with printing outputs ofmore than 40 pages per minute. This paper has lateral holes at itslongitudinal edges for transport and for monitoring the position of thepaper. It is thereby driven by sprocket tractors that engage into thelateral transport holes. This paper often also has transverseperforations along which the individual pages are separated from oneanother.

The margin perforation is particularly employed when processingpre-printed paper. Given this paper, the information subsequentlyapplied in the electrographic printer, for example data that are printedon a pre-printed form, should come to lie as exactly as possible atpredetermined locations of the pre-printed form. For positionally exactprinting, the position of the paper web in the conveying direction mustbe exactly adjusted to or, respectively, synchronized with the drivethereof or, respectively, the movement of the photoconductor drum.

For exact positioning of such paper, the first page of the paper web isplaced exactly at a specific position with respect to the sprockettractors. A page start mark of the pre-print or, respectively, thetransverse perforation thereby exactly prescribes the beginning of thepage. All further pages are automatically exactly positioned due to theconstrained guidance by the tractor sprocket when the first page wasproperly inserted.

The feed of the perforated paper usually ensues in a specific gridcorresponding to the hole spacings, for example in a ½ inch grid or in a⅙ inch grid. The paper web is then not moved continuously butstep-by-step by a multiple of the grid spacing.

There is frequently also the demand in the high-performance printingfield to be able to employ roll paper that does not comprise such marginperforations in printers for continuous-form paper. Both economic aswell as ecological considerations contribute to this demand. Whenprinting margin perforated paper, namely, a processing step wherein themargin strips are removed from the printed page is necessary, wherebythe waste that thereby arises must be disposed of.

For example, Published International application WO 95/19929 A1discloses a printer that is suitable for processing roll paper withoutmargin perforations. A first seating edge, which prescribes the lateralposition of the paper, as well as stabilization rollers, and anunder-pressure brake and a roller arrangement with a loop-drawing meansare provided in this printer for the exact transport of the paper.

Even though continuous form papers both with as well as without marginperforation can be fundamentally processed with such a device, problemsarise when printing forms. When one wishes to process pre-printed paperwith such a printer, then no direct allocation of the pre-printed areato the information to be subsequently printed is possible. As a resultthereof, the information to be subsequently printed cannot be fittedinto the pre-print positionally correct.

Causes of mispositioning are, for example, fluctuations in the paperlength that derive from different ambient temperatures or differentdegrees of moisture of the paper web. Such fluctuations can amount to upto a few millimeters per page. Deviations in the print image on thisorder of magnitude are not acceptable when printing forms.

Added thereto given tractor-less friction drives is the problem that thetransport precision in the feed direction cannot always be adhered to.For example, slippage between the drive drum and the paper web ormanufacturing tolerances of the drive mechanism can contribute thereto.

German Patent document DE 19 37 699 A likewise discloses a frictiondrive for data printers. A sensor that recognizes a pre-printed mark atthe edge of the form is provided given this drive. A reallocation of theline height to the printing location is undertaken with the sensorresult with the respective start of the form. What is disadvantageousabout this drive is that a mark adapted to the sensor must bepre-printed at a specific position of the form so that the controlfunction can be implemented.

U.S. Pat. No. 4,732,501 A discloses a printer wherein a recording mediumweb is transported with a first, slower speed in an insertion mode. Inthis mode, the operator can align the web within the drive before theprinter switches into a printing operation mode with a second, highertransport speed. The switching between these two speeds can becontrolled by a sensor that detects an edge of the recording medium webat a specific position. No specific measures, however, are provided inthis printer for processing pre-printed recording media.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and anapparatus for controlling a tractorless drive for web-shaped recordingmedia with which pre-printed recording media can be transported in apositionally exact manner.

This object is achieved by the method for controlling a tractor-lessrecording medium drive in, in particular, an electrographic printer thatoutputs information on a pre-printed, web-shaped recording medium,whereby the recording medium comprises an identical optical markingpage-by-page, including the following steps: a) the leading edge of therecording medium is placed at a predetermined insertion mark of theprinter in an input region; b) the recording medium is transported aprescribed length along a conveying direction with a first, relativelyslow speed by a transport motor; c) a sensor senses a predeterminedregion of the recording medium during the transport event and sendssensing signals to an evaluation means; d) the evaluation meansinvestigates whether the sensing signals agree with the identifier ofthe marking; e) the transport length lying between two successive,identical markings is identified by the evaluation means as value for apage length; and e) the printing event is initiated with a second,relatively high transport speed and the transport is controlled with theidentified value for the page length. The present invention alsoachieves the objectives by providing an apparatus for controlling atractor-less recording medium drive in, in particular, an electrographicprinter that outputs information on a pre-printed, web-shaped recordingmedium, whereby the recording medium comprises an identical opticalmarking page-by-page, having: a) control means that drive the transportmotor such that the recording medium is transported a prescribed lengthalong a conveying direction with a first, relatively slow speed; b) asensor that senses a predetermined region of the recording medium duringthe transport event and sends sensing signals to an evaluation means,whereby c) the evaluation means investigates whether the sensing signalsagrees [sic] with the identifier of the marking and the transport lengthlying between two successive, identical markings is identified as valuefor a page length; and d) the printing event is initiated with a second,relatively high transport speed and the transport is controlled with theidentified value for the page length. Advantageous embodiments of theinvention are the improvements to the method, including that theevaluation means comprises a memory in which at least one value for astandard page length is stored; and in that the value for a page lengthdetermined with the sensor is checked with the standard value or thestandard values for plausibility before the determined value isidentified as value for the page length. Following the identification ofthe page length, the recording medium is moved at least once oppositethe conveying direction such that the first mark comes to lie in theactive region of the sensor and, taking the identified page intoconsideration, is subsequently accelerated anew to the second mark,whereby the characteristic drive values thereby employed are stored foremployment after a print stop. The sensor is preferably sensitized tothe markings and/or to the background of the markings before it sensesthe recording medium for markings. The sensor ensues in that therecording medium is transported at least once in the direction of andopposite to the conveying direction, and the evaluation means checksduring this forward and return motion to see whether and when the sensoroutputs a signal. In one embodiment, the sensitization of the sensorensues spectrally. The sensitization of the sensor may ensues in view ofthe shape of the marking. A sensor setting value determined during thesensitization is preferably stored. The information-containingcomponents, particularly text components of pre-printed forms may beemployed as the marking. The recording medium is typically paper.

It is provided in the invention to apply the leading edge of thepre-printed web of the recording medium provided with markings to apredetermined insertion mark in an input region of the printer.Subsequently, the recording medium web is transported a predeterminedlength along a conveying direction by a transport motor with a first,relatively low speed. A sensor thereby senses a predetermined region ofthe paper and sends sensor signals to an evaluation means. Thisevaluates the signals and checks whether they can be allocated to apredetermined mark. The transport length lying between two successivemarks is then identified by the evaluation means as a value for a pagelength. Finally, the printing event is initiated with a second,relatively high transport speed and controlled with the identified valuefor the page length.

What the invention enables is that the drive for the web of therecording medium is already synchronized to the page length after a feedof one page. Positional deviations of the web that occur due toimprecise insertion of the paper web or due to increased slippagebetween the drive and the web are thereby already compensated after thefirst printed page. As a result of the invention, it is also possible totransport recording medium webs that contain indefinite pre-prints in apositionally exact manner. For example, the pre-prints can be indefinitein terms of type, color, shape, the size (length) or the position on therecording medium. The control requires only a negligible time fortransient response. Maculature, i.e. excess, unprinted paper is largelyavoid as a result thereof. The printing already ensues in a positionallyexact manner within the pre-print with the first printed page.

In a preferred exemplary embodiment of the invention, the evaluationmeans comprises a memory in which at least one value for a standard pagelength is stored. The value for a page length determined with the sensoris checked against the standard value or the standard values forplausibility before the identified determined a value is identified asvalue for the page length. As a result thereof, it is possible tosynchronize the drive exactly with the page length of the pre-print evenwhen the page length deviates from the theoretical rated value.

In another advantageous embodiment of the invention, the sensor issensitized for the markings and/or for the background of the markings.It is also advantageous to arrange the sensor so as to be displaceabletransversely relative to the recording direction. The mark can then lieat an arbitrary location of the form. Even constituent parts of the formsuch as texts, graphics or window cut-outs can then be employed as amark. The sensor of the invention can thus be adapted to the respectivecontent of the form in that it is sensitized for a selected item ofinformation.

In particular, the sensor can be of an optoelectronic type; thesensitization in a preferred exemplary embodiment then ensues forspecific colors of the background or, respectively, of the mark.Alternatively or additionally, the sensitization of the sensor can alsoensue in view of a geometrical shape of the markings or in view of thesurface structure of the recording medium web. For example, the markscan thereby be notches provided in paper webs or window cut-outs in formoriginals. A sensor setting value determined in the sensitization ispreferably stored and re-employed for later measurements.

The sensitization of the sensor preferably ensues in that the paper istransported at least once in the conveying direction and once oppositethe conveying direction, whereby the evaluation means checks during thisforward and return motion whether and when the sensor outputs a signal.It can thereby be provided that a plurality of cycles or forward andreturn motions are implemented and that a setting value at the sensor ismodified after every cycle. The sensor setting values that are finallydetermined can then be stored and re-employed for later sensitizationevents. A self-learning system can thereby be generated in that acertain plurality of the setting values that are employed most oftenand/or most recently is employed at the beginning of a sensitizationprocedure.

What is particularly achieved with the inventive starting procedure isthat the printing event can begin with the first page that follows thepage required for the sensitization of the sensor.

The inventive procedure can be largely automated. Operating errors uponinsertion of the paper are thereby largely precluded or, respectively,can be compensated. The procedure requires only little time, as a resultwhereof the effective printing time of the printer is high.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are explained in greater detailbelow on the basis of some Figures.

FIG. 1 is a schematic side view in section of a printer with atractorless paper drive;

FIG. 2 is a side section through a drive unit;

FIG. 3 is a front perspective view of the drive unit;

FIG. 4 is a bottom perspective view of sensor arrangement;

FIG. 5 is a block circuit diagram for the control of the drive with aschematic representation of the recording medium;

FIG. 6 is a flowchart for controlling the drive; and

FIG. 7 is a flowchart for sensitizing the sensor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The printer device shown in FIG. 1 takes a web-shaped recording medium 5of paper from a paper input container 1 or from a supply reel 11. In theroll operation, the paper web 5 is supplied via a loop 12 to adeflection means 2 and is subsequently guided in a web pre-centeringmeans 3 along a seating edge to friction drive rollers 4. Subsequently,it is pulled by a drive 8 via an under-pressure brake 6 that isconnected to a vacuum pump 7 that generates the under-pressure. Thepaper web 5 is decelerated due to the under-pressure, and the tension ofthe paper web 5 is thereby increased. The paper web 5 runs all the morestable in a conveying direction A, the higher the tension is, i.e. itslides laterally out of the rated paper conveying direction to a lesserextent. Following the under-pressure brake 6, the paper web 5 passesthrough a stabilization zone that is composed of a plurality ofdeflection rollers 9 and a loop-drawing means 10. The paper web 5 wrapsthe deflection rollers 9 by at least 180°, as a result whereof the paperweb is laterally stabilized even further.

Before the paper web 5 is supplied to a printing unit 14, a sensorarrangement 17 optically senses the paper 5. The sensor arrangement 17is thereby designed such that it can still sense the widest paper 5 tobe processed in the printer over its full width. The width of the sensorarrangement 17 is thus matched both to the mechanical components for thepaper transport as well as to the parameters of the printer means 14that define the printable width. In the present exemplary embodiment,the paper width that can be processed extends from 6.5 inches (165 mm)to 19 inches (482.6 mm). Details of the sensor arrangement 17 aredisclosed in German Patent Application Serial Number DE 197 49 676.8filed by the assignee, the content thereof being herewith incorporatedinto the present specification by reference.

The paper web 5 is supplied from the sensor arrangement 17 to a transferprinting station via a drive unit 13. In the illustrated exemplaryembodiment, the transfer printing station comprises a photoconductordrum 16 that interacts with a corotron means 16 a. In a known way, thephotoconductor drum 16 is thereby charged with information correspondingto an image by means of light, as a result whereof a charge image isapplied. Subsequently, it picks up a magnetized or charged toner that istransferred onto the paper web 5 in the transfer printing area.Subsequently, the corotron means 16 in turn discharges the correspondingregion of the photoconductor drum 16, so that this can be written anewwith information. The corotron means 16 a thereby functions in a wayknown per se such as disclosed, for example, European Patent document byEP 0 224 820 B1.

In the illustrated example, the sensor arrangement 17 is arranged in theregion of the paper feeder means 15; however, it can also be providedinside the printing unit 14. The paper web 5 is transported in the paperconveying direction A.

FIG. 2 shows the drive unit 13 arranged in the region of the transferprinting station or, respectively, of the photoconductor drum 16 of theelectrophotographic printer in greater detail.

A roller arrangement 20 presses against the drive drum 40 with apredetermined force. As a result thereof, the paper 5 which istransported between the drums 40 and 20 is moved by the drive drum 40 asa result of frictional engagement (friction). The drive drum 40 is inturn connected to the stepping motor 41 via a toothed belt drive. Theentire drive unit 13 is flanged to a printer housing via the bearingblock 44. A common bearing axis 42 is seated at the bearing block 44 bythe ball bearing 43, the common bearing axis accepting, on the one hand,the rotational motion of the drive drum 40 and, on the other hand,enabling a swivel motion of the drive elements around the swivellingaxis B. In order to enable the swivel motion, the drive components aremounted on a carrier plate 47 that is connected to the bearing block 44via a gas compression spring 49 as well as via the bearing axis 42.

Threads 45 located in the bearing block 44 serve for the acceptance offastening screws that are guided through the printer housing. The entiredrive unit is adjustable within the printer housing via guide surfaces46. The carrier plate 47 is in turn adjustable relative to the bearingblock 44, whereby a first adjustment screw 51 and a second adjustmentscrew 52 against which cylinder pins at the carrier side strike areprovided in the bearing block 44.

The gas compression spring 49 is connected to the carrier 47 by thescrew connection 50 and is connected to the bearing block 44 by thescrew connection 48. The carrier 47 and the bearing block 44 can belocked relative to one another with the locking means 54.

A paper web 5 that is introduced into the drive unit 13 between thedrive drum 40 and the counter-pressure drum 20 is guided to a papersensor 55 by a guide plate 53. The paper sensor 55 senses the paper 5over the entire width of the printable region of the photoconductor drum16, as a result whereof both the lateral paper edges as well aspotential margin perforations of the paper web 5 can be recognized. Inthe region of the transfer printing zone of the printer unit, the paperis pressed against the surface of the photoconductor drum 16 byspring-seated swivel jaws 56. A known corotron means 57 generates ahigh-voltage with which the toner located on the photoconductor drum 16is drawn to the paper. Deflection rollers 58 move the paper 5 forward toa mark sensor 59 that recognizes any printing or cutting marks that maybe present on the paper web 5. Grounded electrical connections 61(anti-static plates) carry off any residual electrical charges locatedon the paper 5.

When margin perforated paper 5 is transported with the paper transport,the margin perforation can be sensed with a pin feed wheel 60.

FIG. 3 shows a perspective illustration of the paper drive 13. Inparticular, the cylinder pin 66 which is mounted at the carrier plate 47that interacts with the adjustment screw 52 screwed in the bearing block44 as well as the screw connection of the gas compression spring 49 canbe seen therefrom.

The paper 5 is guided by a guide surface 69 above the deflection drums58. The sensing of the paper 5 with the mark sensor 59 also ensues inthis region. Further, a seating rule 65 is provided in this region, thisbeing employed for the printer start. Newly inserted paper 5 thatcomprises margin perforations thereby has a page start placed against amarking 65 a of the rule 65 that corresponds to the page length, themargin perforation is brought into engagement with the engaged pin wire60, and the printing operation is initiated. The pin feed wheel 60 is acomponent part of a sensor arrangement that is described in greaterdetail in FIG. 4.

In the transfer printing area, a drive motor 68 pulls a corotron wirefrom the corotron wire cassette 57 according to the page width to beprinted. The mark sensor 59 is displaceable in the direction E along arod 73. A plate covers the drive motor 41 and serves, in particular, aselectromagnetic shielding. Corresponding to the front bearing block, aback bearing block 67 is also provided, this being likewise secured tothe printer housing.

FIG. 4 shows the pin feed wheel sensor 85 that embraces the pin feedwheel 60. In the illustrated position, the pin feed wheel 60 is pivotedout, i.e. the pins do not project beyond the paper-guidance plane 69.The pin feed wheel 60 can be pivoted in or, respectively, out in thedirection F with the actuation lever 86. The pin feed wheel 60 is seatedon a shaft 87 that likewise carries a gearwheel 88. A magneto-resistivesensor 91 detects pulses of the metal cogs of the gearwheel 88.

These pulses can be unambiguously allocated to the rotational motion ofthe pin feed wheel 60, so that a sensing of the margin perforation ofpaper can thus ensue, the paper running over the paper plane 69 andbeing in engagement with the pin feed wheel 60. Consequently, the speedof the paper web 5 as well as its position with reference to thetransport grid of the drive mechanism can be determined from thesepulses. The signals of the sensor 85 are therefore employed as inputsignals for an anti-slip control of the paper drive. The sensor assembly89 is electrically connected to a device controller (FIG. 5) for thispurpose.

A second magneto-resistive sensor 92 detects whether the pin feed wheelsensor 85 is in the swivelled-in or swivelled-out position with respectto the paper guidance plane 69. To this end, it interacts with a magnet93 that is mounted on the guide surface 69. The entire pin feed wheelsensor 85 can be latched in the swivelled-out or, respectively,swivelled-in position with a latch mechanism 90.

FIG. 5 shows electronic control components of the printer as well astheir collaboration with the drive mechanism and sensors. The drive unit13 has a drive controller 100 that is connected via a general data bus112 to a higher-ranking printer controller 101. The operator can inputcommands via a control panel 105. The drive controller 100 receives thesignals of the paper width sensor 17 or, respectively, 55 via theinterface 104 thereof. It determines both the paper width as well as thetype of paper, i.e. whether margin perforations are present, therefrom.The drive controller 100 also receives the sensor signals of the pinfeed wheel sensor 85 via its electronics 103 as well as those of themark sensor 59 via its electronics 107. The speed of the paper web 5 iscalculated in the drive controller 100 from the signals of thecomponents 103 or, respectively, 107. The result is employed foranti-slip control of the stepping motor drive 102. The rated speedsignals are thereby supplied by the printer controller 101.

One proceeds as follows for preparing for a printing event (startoperating mode) after the printer is turned on or after insertion of anew paper web 5:

A paper web 5 is manually drawn into the printer up to the drive unit 13by the various components of the unit. Thereat, the leading edge 110 ofthe paper web 5 thread up to the guide surface 69 in the region of therule 65.

When the paper web 5 comprises a margin perforation, this is broughtinto engagement with the pins 82 of the swivelled-in pin feed wheel 60.When the paper web does not comprise margin perforation, the pin feedwheel 60 is placed into the swivelled-out condition.

The feed of the paper web 5 already ensues via the drive motor 41 in theregion of the rule 65. The operator thereby determines the direction ofthe feed (forward/backward) in order to exactly align the start of apage with a marking of the rule 65 corresponding to the page length. Thefeed thereby ensues relatively slowly and in small grid steps.

Given margin perforated paper 5, the transport steps in the startoperating mode amount to only fractions of the hole grid spacing, whichtypically amounts to ⅙ inch (approximately 4.3 millimeters). The stepwidth amounts, for example, to {fraction (1/20)} grid spacings(approximately 0.21 millimeter). Given this type of transport, the speedor the position of the paper 5 is acquired with the pin feed wheelsensor 85 and 15 is compared to the speed or position of the drive motor41. Any slip, i.e. a discrepancy between these two speeds or positions,which occurs is thereby identified and compensated by additional advance(additional steps in conveying direction) by the drive controller 100.

When paper 5 without a margin perforation is employed, the positionand/or speed of the paper web 5 are sensed with the mark sensor 59 whoseelectronic components 107 deliver corresponding signals to the drivecontroller 100. Instead of the above-described sensor 59, other, knownsensors can be employed for measuring speeds, for example the sensordisclosed by German Patent document DE 44 28 156 A1 or the sensordisclosed by U.S. Pat. No. 5,204,620.

The procedure for the correct insertion and conveying of the paper 5 aswell as for sensitizing the mark sensor 59 is described below withreference to FIGS. 5, 6 and 7.

First, the paper web 5 is roughly positioned with its leading edge 110in the region of the sensor 59 or, respectively, of the rule 65. Theoperator is thereby granted a certain tolerance of, for example, a fewmillimeters by which the position of the leading edge (page start) isallowed to deviate from the rated position. A corresponding insertionmarking 65 a is provided on the rule 65 for the rated position. Variousinsertion regulations are possible for this purpose. For example, theinsertion marking 65 a can lie at various locations of the rule 65dependent on the page length. Alternatively, a common insertion marking65 a can also be provided on the rule 65 for various page lengths.Finally, the insertion marking 65 a can also lie directly under thesensor 59, i.e. at its sensing point. (Step S1). The page length onwhich the pre-print is based is then input at the control panel 105 ofthe printer and the value is stored in the memory 106 (step S2).

A specific information that is intended to serve as a mark 109 is thenselected from the forms that are pre-printed on the paper web 5. Thismark 109 can be both a text as well as graphic information, whereby itis also conceivable to employ a modified surface structure, for examplea window cut-out punched into forms. The sensor 59 is matched to therespectively selected mark information. In the present exemplaryembodiment, an opto-electronic sensor 59 is employed that has a highcontrast sensitivity as well as a color sensitivity. If the windowcut-outs were to be employed as the mark information, then, for example,a mechanical sensing device or an ultrasound sensor could also besuitable as the mark sensor 59. An information 108 of the form thatoccurs only once per form page with reference to the feed direction Ashould be employed as the mark 109. When it occurs more often, then theevaluation electronics 107 of the sensor 59 or, respectively, the unitcontroller 100 must be in the position to filter out the repetitionswithin the page, so that the drive can be respectively exactly regulatedto the page start information.

When characteristic properties of the mark 109 such as the magnitude ofthe contrast transition, color of the background, color of the markinformation, etc., are known, these can likewise be input via thecontrol panel 105 and stored in the memory 106 (steps S3, S4).

The information about the region of the form in which the mark 109 liesis also queried and potentially stored. As a result thereof, a window isprescribed within the form wherein the sensor 59 reacts to the markinformation.

By prescribing a mark window, it is also assured that the markinformation is allocated to the correct page, even when one and the samemark 109 repeatedly occurs identically on a form page. The data transferbetween control panel 105, higher-ranking printer controller 101 andunit controller 100 ensues via the data bus 112.

The characteristic data about the mark 109 can also be offered by theprinter controller 101 insofar as it obtains these data in some otherway. For example, the data can be co-supplied in the header area of aprint job. An operator who compiles this print job on a higher-rankingcontrol computer (print server) can attach these particulars to theprint job at this stage, as a result whereof the printing event isautomated further upon arrival of the print job.

When the characteristic values of the mark 109 are not known, anautomatic procedure 111 is started with which the unit controller 100fully automatically acquires and stores the characteristic values of themark 109. What is referred to as this sensitization procedure isdescribed in greater detail later in conjunction with FIG. 7.

Returning to FIG. 6, a step-by-step advance of the drive 13 in anextremely small grid ensues that corresponds to only {fraction (1/20)}of the hole grid spacing of margin perforated paper 5. In this phase,the actual page length of a form is identified on the paper web 5. Acounter n is incremented by the value 1 with every feed step (S5) and acheck is subsequently carried out to see whether the mark 109 wasrecognized (step S7). If not, another forward step is undertaken and thecounter n is again incremented (steps S5, S6). When the mark has beenrecognized, the page length value is taken from the memory 106 and anadvance by barely one page length is undertaken, i.e. by a number ofsteps that is smaller by x than the number of steps of the page length(n_(s1), step S8).

Subsequently, another step forward is respectively undertaken and thestep counter n is incremented by the value 1 (steps S9, S10).Subsequently, another check is carried out to see whether the next,following mark 109 was recognized (step S11); if not, another advanceand incrementation are undertaken; if yes, then the value n is retainedas a current page length value and is stored in the memory 106 (stepS12). Subsequently, a “ready to print” message is generated (step S13).Before the printing event can be started on the photoconductor drum 16,the paper 5—using the previously identified values for the page lengthand for the mark position—is also positioned attitudinally correctrelative to the photoconductor drum 16.

With the described method, both the exact position of the pre-print onthe paper 5 relative to the print element as well as the actual formlength which is important for the paper transport can be determined. Theprinting event can be started immediately with high registrationprecision with the exact information about the position of the forms andthe length of the forms.

For sensitizing the sensor 59 (FIG. 7), the sensor 59 is first adjustedonto the background of the paper web 5 in the procedure 111. To thatend, the unprinted paper web 5 is sensed by the sensor 59 and the sensorsignals are read and intermediately stored (step S15). Subsequently, acheck is carried out to see whether the background information exhibitsan adequately high signal strength (step S16). When not high enough,sensor parameters such as gain, illumination intensity or the like aremodified and the step S15 is repeated until the sensor signals areadequately high. Subsequently, the paper web 5 is moved forward (stepS17) in the recording direction until the sensor 59 detects anadequately big marking to be distinguished from the background (stepS18). When, given a predetermined plurality of feed steps, no mark 109can be identified with adequate precision, then the paper web 5 is againcompletely retracted, the settings at the sensor 59 are modified and arenewed search run is started. The sensor settings are thereby modifieduntil the sensor 59 recognizes a mark 109. The operator can abort thesearch procedure at any time. In addition to the brightness of the lightsources integrated in the sensor 59, the spectral distribution (red,green, blue) thereof can also be modified. As a result thereof, coloredmarkings can be reliably recognized by the sensor 59 in front of acolored background. The identified values for the background and themark 109 are stored in the memory 106 (step S19). Following the stepS19, the start procedure is continued with the step S8. An instructioncommand, “return to main”, is output for this purpose (step S20).

During the normal operating mode, wherein the printing process isrunning, the paper web 5 is processed page-exactly, whereby completepages are always printed. Slippage between the drive 13 and the paperweb 5 in this operating mode is acquired in a way similar to that in thestart operating mode, but is not compensated not on the basis ofadditional feed but by a higher speed of the drive motor 41. When paperhaving margin perforation is employed, the margin holes are continuouslysensed by the pin feed wheel sensor 85 and the sensor signals areemployed for anti-slip control. When paper 5 without margin perforationis employed, then the marking 109 is sensed page-by-page and thissensing result is employed for anti-slip control. This page-by-pagesensing can also be employed instead of or in addition to the sensing ofthe pin feed wheel sensor 85 given margin perforated paper 5. What is ofconcern given this page-by-page control version, however, is that thedrive 13 is so exact that no great dislocations of the print image arepresent within a page at the page end (or, respectively, shortly beforethe mark 109 of the next page).

When a printer stop is necessary proceeding from the ongoing printingmode, then the drive controller 100 does not effect an immediate stop ofthe drive but a stop at the next page change. As a result of thismeasure, the allocation of the steps of the drive motor 41 to the sensedmarks 109 is very well maintained.

Given re-assumption of the printing event following a print stop, thedrive is initially moved a few steps or even page lengths opposite theprint transport the direction A and is then accelerated in direction A.The acceleration event can thereby ensue corresponding exactly to themotion of the start operating mode. Characteristic values about thenecessary feed compensation can therefore likewise be stored in thestart phase and can be employed in the re-assumption of an abortedprinting event.

What is achieved by these measures is that the printing mode can becontinued with page precision after a print stop and maculature isavoided. Since the page length of the paper web 5 is known from thestart operating mode, its value can be re-employed following a printstop. The procedure for determining the page length (FIG. 6) can then beforegone.

When it is necessary to re-insert the paper web 5 following a printstop, for example following a tearing of the paper, then one proceeds asfollows: first, the operator positions the new paper web roughly at therule 65 in the insertion area. Subsequently, the paper web 5 istransported forward by the drive unit 13 with a first, slow speed untilthe mark sensor 59 detects a mark 109. On the basis of this identifiedmark position and the page length determined before the print stop, thepaper web 5 is again positioned page-correctly relative to the printingstation 14 and the printing process is continued.

In another, improved embodiment of the start operating mode, the paperweb 5 is transported back and forth between the detected marks 109 onceor repeatedly relative to the mark sensor 59 following theidentification of two successive marks 109. As a result thereof, dynamicconditions in the acceleration of the paper web 5 can be determined moreexactly, and the drive control in the acceleration phase is improvedfurther. In particular, a optimum speed curve of the drive, with whichthe slippage is largely compensated, is thereby identified. These valuescan be stored job-specifically or, respectively, paper-specifically andemployed for an additional speed control of the drive givenre-assumption following a print stop.

Using the signals of the paper width sensor 17, the drive controller 100can also determine whether and which type of paper is introduced intothe printer. To that end, the drive motor 41 is repeatedly moved forwardand back and the sensor signals are interpreted. When one or more holesare recognized, then a perforated paper web 5 is assumed. An automaticalignment onto the hole grid can then also ensue automatically on thebasis of the recognized hole positions.

Even though the invention was mainly described with exemplaryembodiments that employ paper as the recording medium, it isself-evident that it can also be applied in conjunction with otherrecording media such as, for example, foils. It is also not bound tospecific imaging means such a photoconductor drums but can also beemployed in combination with band-shaped transfer means such aphotoconductor bands or magnetographic devices.

By providing a plurality of control marks on a form page, the controlprecision within a page could also be enhanced given paper that is freeof margin perforations. Using a motor drive that acts on the mark sensor59 transversely relative to the paper conveying direction (direction Ein FIG. 5) in the start operating phase, what can also be achieved isthat the sensor 59 also automatically detects the mark in thisdirection. The degree of automation and, thus, the operatingdependability could thereby be further enhanced.

A further automation can also be achieved when the mark sensor 59 ismotor-displaced along the axis 73 in direction E for being sensitized(see FIG. 3).

Even though electrophotographic printers have been described in theexemplary embodiments, the invention can also be applied to printerswith different recording principles, for example to ink jet printer orthermal transfer printers.

Although other modifications and changes may be suggested by thoseskilled in the art, it is the intention of the inventors to embodywithin the patent warranted hereon all changes and modifications asreasonably and properly come within the scope of their contribution tothe art.

We claim:
 1. A method for controlling a tractor-less recording mediumdrive in an electrographic printer that outputs information on arecording medium that is web-shaped, the recording medium having anidentical optical marking on pages, comprising the following steps: a)placing a leading edge of the recording medium at a predeterminedinsertion mark of the electrographic printer in an input region; b)transporting the recording medium a prescribed length along a conveyingdirection with a first relatively slow speed by a transport motor; c)sensing a predetermined region of the recording medium during thetransporting step and sending sensing signals to an evaluator; d)investigating whether the sensing signals agree ] with an identifier ofthe marking; e) identifying a transport length lying between twosuccessive identical markings by the evaluator as a value for a pagelength; and f) initiating a printing event with a second relatively hightransport speed and controlling transport with the identified value forthe page length.
 2. A method according to claim 1, wherein saidinvestigating step includes: storing at least one value for a standardpage length in a memory; and checking the value for a page lengthdetermined with the sensor against at least one standard value forplausibility before the determined value is identified as a value forthe page length.
 3. A method according to claim 1, further comprisingthe steps of: following said identifying step for identification of thepage length, moving the recording medium at least once opposite theconveying direction such that the first mark comes to lie in an activeregion of the sensor; taking the identified page length intoconsideration, subsequently accelerating to the second mark; and storingcharacteristic drive values for employment after a print stop.
 4. Amethod according to claim 1, further comprising the step of: sensitizingthe sensor so that it is capable of sensing at least one of the markingsand a background of the markings before said sensor senses the recordingmedium for markings.
 5. A method according to claim 4, wherein saidsensitizing step includes: transporting the recording medium at leastonce in the conveying direction and opposite the conveying direction;and checking the evaluation means during this forward and return motionto see whether and when the sensor outputs a signal.
 6. A methodaccording to claim 4, wherein said step of sensitizing the sensorprovides that said sensor is spectrally sensitive to said markings orsaid background.
 7. A method according to claim 4, wherein said step ofsensitizing the sensor provides that said sensor is sensitive to a shapeof the marking.
 8. A method according to claim 4, further comprising thestep of: storing a sensor setting value determined during said step ofsensitizing.
 9. A method according to claim 1, further comprising thestep of: utilizing information-containing components of pre-printedforms as the marking.
 10. A method according to claim 1, wherein paperis employed as said recording medium.
 11. An apparatus for controlling atractor-less recording medium drive in an electrographic printer thatoutputs information on a recording medium that is web shaped, therecording medium having an identical optical marking on pages,comprising: a transport motor; a controller that drives the transportmotor such that the recording medium is transported a prescribed lengthalong a conveying direction with a first relatively slow speed; anevaluator; a sensor that senses a predetermined region of the recordingmedium during transport and sends sensing signals to said evaluator;said evaluator being operable to investigate whether the sensing signalsagree with an identification of the marking and identify a transportlength lying between two successive identical markings as a value for apage length; and said controller initiating printing with a secondrelatively high transport speed and controlling transport with theidentified value for the page length.
 12. An apparatus according toclaim 11, wherein said evaluator includes a memory in which at least onevalue for a standard page length is stored; and said controller beingoperable to check that the value for a page length determined with thesensor is the standard value or the standard values for plausibilitybefore the determined value is identified as a value for the pagelength.
 13. An apparatus according to claim 11, wherein said controlleris operable such that, following the identification of the page length,the recording medium is moved at least once opposite the conveyingdirection such that the first mark comes to lie in the active region ofthe sensor and, taking the identified page into consideration, issubsequently accelerated anew to the second mark, characteristic drivevalues thereby employed being stored for employment after a print stop.14. An apparatus according to claim 11, said sensor being sensitized toat least one of the markings and the background of the markings beforesensing the recording medium for markings.
 15. An apparatus according toclaim 14, wherein the sensitization of the sensor ensues with thecontroller such that the recording medium is transported at least oncein the conveying direction and opposite the conveying direction; and theevaluator checks during this forward and return motion to see whetherand when the sensor outputs a signal.
 16. An apparatus according toclaim 14, wherein the sensor is spectrally sensitized.
 17. An apparatusaccording to claim 14, wherein the sensor is sensitized in view of ashape of the marking.
 18. An apparatus according to claim 14, whereinsaid controller includes a storage wherein a sensor setting valuedetermined during the sensitization of the sensor is stored in thecontroller.
 19. An apparatus for tractor-less transport of a recordingmedium in a printer device, the recording medium having markings forpages, comprising: a controller that drives the transport motor suchthat the recording medium is transported a prescribed length along aconveying direction with a first relatively slow speed; an evaluator; asensor that senses a predetermined region of the recording medium duringtransport and sends sensing signals to said evaluator; said evaluatorbeing operable to investigate whether the sensing signals agree with anidentifier of the marking and identify transport length lying betweentwo successive identical ones of the markings as a value for a pagelength; and said controller initiating printing with a second relativelyhigh transport speed and controlling transport with the identified valuefor the page length.
 20. A printer having an apparatus for controlling atractor-less recording medium drive in an electrographic printer thatoutputs information on a recording medium that is web shaped, therecording medium having an identical optical marking on pages,comprising: a transport motor; controller that drives the transportmotor such that the recording medium is transported a prescribed lengthalong a conveying direction with a first relatively slow speed; anevaluator; a sensor that senses a predetermined region of the recordingmedium during transport and sends sensing signals to said evaluator;said evaluator being operable to investigate whether the sensing signalsagree with an identifier of the marking and identify transport lengthlying between two successive identical markings as a value for a pagelength; and said controller initiating printing with a second relativelyhigh transport speed and controlling transport with the identified valuefor the page length.
 21. A method for controlling a tractor-lessrecording medium drive for a web-shaped recording medium in anelectrographic printer, the web-shaped recording medium having anidentical optical marking on pages, comprising the step of: transportingthe recording medium first with a first speed, acquiring a transportlength of the recording medium lying between two successive identicalmarkings and identifying the transport length as a value for a pagelength with an evaluator and a sensor; and for printing, transportingthe recording medium with a transport speed that is higher compared tothe first speed and controlling the transporting of the recording mediumutilizing the identified value for the page length.